The invention relates to a brake cylinder for pneumatically actuated vehicle brakes, in particular for commercial vehicles.
In heavy commercial vehicles, the parking brake is actuated by what are known as spring force accumulator cylinders (spring-loaded cylinders). Here, the brake actuating force is generated via spring force, with the result that the requirements for a mechanically actuated parking brake are satisfied.
Since the spring force accumulator cylinders are, as a rule, designed to generate very high forces, manual release in the operating case is no longer appropriate. In the case of pneumatically actuated brakes, the parking brake is therefore released by means of compressed air.
In order to make this possible, spring force accumulator cylinders are, as a rule, equipped with a release piston. It is possible by way of this piston, if compressed air is introduced, to compress the spring to such an extent that the brake is released. In order that the parking brake is not engaged while driving, the piston is loaded constantly with compressed air, with the result that the spring cannot be relieved and therefore the parking brake does not start to act.
The most common design is what is known as a combined cylinder. A combined cylinder includes or combines two different brake cylinder types, namely a spring force accumulator cylinder for the parking brake system (PBS) and a compressed air cylinder (usually a diaphragm cylinder) for the service brake system (SBS).
The two cylinders are usually arranged behind one another in an axial direction. The spring force accumulator part, which acts with its piston rod on the piston collar of the diaphragm cylinder and by the latter, in turn, on the brake lever, is arranged behind the diaphragm part of the combined cylinder.
This design requires a relatively large amount of installation space. However, the installation space is being limited increasingly by the introduction of more complex chassis systems, such as independent suspension systems, lightweight axles, etc.
There are therefore efforts to minimize the space requirement for the parking brake cylinder by other designs and methods of operation. To this extent, what is known as a compact combined cylinder affords a more compact design. DE 10 2005 044 708 A1 (corresponding to U.S. Pat. No. 7,523,999 B2) discloses a brake cylinder of this type. In DE '708, the function of the parking brake cylinder is integrated directly into the service brake cylinder. Here, the spring force accumulator spring is no longer actuated via a separate spring force accumulator piston, but rather likewise via the piston of the service brake cylinder. In order to release the parking brake, the SBS piston is loaded for a short time period by way of a special actuation with compressed air.
As described in the preceding text, the parking brake is released as a rule with the aid of compressed air. In addition, however, it also has to be possible to release the parking brake by a manual operation in the case of a pressure loss.
To this end, in the case of conventional combined cylinders, the spring is pulled back with the aid of a threaded spindle (what is known as the “release spindle”). As a result, the function of the service brake cylinder is not impaired.
This cannot be realized in such a simple way in the case of the compact combined cylinder, since the SBS piston and the spring force accumulator spring are connected to one another. If the spring were pulled back by a threaded spindle which is accessible from the outside, the SBS piston would also be blocked and, as a consequence, the SBS cylinder would no longer function.
The object of the invention is to solve this problem with regard to combined cylinders.
According to the invention, a manually actuable release device is provided for releasing the spring force accumulator spring manually, which manually actuable release device makes it possible to cancel the spring force accumulator action in the case of a pressure loss, without impairing the SBS function. Furthermore, it is possible to reestablish the PBS action by a manual operation after the release operation.
The invention is also suitable, in particular, for compact combined cylinders which have a threaded spindle with a quick action thread that is not self-locking. The quick action thread primarily serves to make it possible for the spring force accumulator spring to be locked in what is known as the release position. To this end, the threaded spindle is arrested by way of a pneumatically actuated locking mechanism. When the parking brake is engaged, the locking mechanism is ventilated, as a result of which the threaded spindle can be rotated and the spring force accumulator spring can be relieved.
According to one particularly advantageous embodiment of the invention, the threaded spindle is also used to release the spring force accumulator spring manually. Here, the threaded spindle is set in rotation by an external introduction of force. Since it is a quick action thread which is not self-locking here, the spindle would rotate back again immediately and the spring force accumulator spring would therefore start to act again, for example, if the wrench is moved.
It is therefore necessary for the mechanism to be equipped, in particular, with a direction-dependent locking function or apparatus. According to the various embodiments, the locking apparatus also fulfills further requirements.
The locking apparatus is preferably to be designed such that it is switched off during normal operation of the brake cylinder. Otherwise, it would not be possible to engage the spring force accumulator brake, since the rotation of the threaded spindle in the relief direction of the spring force accumulator spring is suppressed by the direction-dependent locking action.
The locking apparatus is preferably to be designed such that it is possible to rotate the threaded spindle in both directions, in order for the PBS brake to be both released and engaged manually. Here, for safety reasons, the spring force accumulator spring should not be relieved in a single step and an unmeasured way, but rather in a manually measurable way (in an analogous way to the behavior in the case of a conventional spring force accumulator cylinder).
On account of the limited installation space, the locking apparatus is to have as compact and simple a construction as possible. Moreover, the components should be designed in such a way that inexpensive manufacturing is possible, for example by forming technology without the removal of material.
In principle, two different functional principles are contemplated: (a) first frictionally engaging systems based on a free wheel principle, and (b) second positively engaging systems based on a ratchet mechanism.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.